/*
 * Copyright (c) CraftWorks Inc. All rights reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.craftworks.util;

/**
 * An implementation of CRC32 algorithm (fast version)
 *
 */
public final class CRC32
{
    private CRC32() {}

    /**
     * 计算输入数据的CRC32校验值。
     *
     * @param data 待校验数据。
     * @return CRC32校验值。
     */
    public static long checksum(byte[] data)
    {
        return checksum(data, 0, data.length);
    }

    /**
     * 计算输入数据的CRC32校验值。
     *
     * @param data 包含待校验数据的缓冲区。
     * @param offset 数据在缓冲区内的起始偏移量。
     * @param length 数据长度。
     * @return CRC32校验值。
     */
    public static long checksum(byte[] data, int offset, int length)
    {
        long crc;
        byte idx;

        crc = 0xFFFFFFFFL;
        for (int i = 0; i < length; i++)
        {
            idx = (byte) ((crc >>> 24) ^ data[offset + i] & 0xFF);
            crc = (crc << 8) ^ CRCTABLE[(idx & 0xFF)];
        }
        crc = crc & 0xFFFFFFFFL;

        return crc;
    }

    public static final long[] CRCTABLE =
    {
        0x00000000L, 0x04C11DB7L, 0x09823B6EL, 0x0D4326D9L,
        0x130476DCL, 0x17C56B6BL, 0x1A864DB2L, 0x1E475005L,
        0x2608EDB8L, 0x22C9F00FL, 0x2F8AD6D6L, 0x2B4BCB61L,
        0x350C9B64L, 0x31CD86D3L, 0x3C8EA00AL, 0x384FBDBDL,
        0x4C11DB70L, 0x48D0C6C7L, 0x4593E01EL, 0x4152FDA9L,
        0x5F15ADACL, 0x5BD4B01BL, 0x569796C2L, 0x52568B75L,
        0x6A1936C8L, 0x6ED82B7FL, 0x639B0DA6L, 0x675A1011L,
        0x791D4014L, 0x7DDC5DA3L, 0x709F7B7AL, 0x745E66CDL,
        0x9823B6E0L, 0x9CE2AB57L, 0x91A18D8EL, 0x95609039L,
        0x8B27C03CL, 0x8FE6DD8BL, 0x82A5FB52L, 0x8664E6E5L,
        0xBE2B5B58L, 0xBAEA46EFL, 0xB7A96036L, 0xB3687D81L,
        0xAD2F2D84L, 0xA9EE3033L, 0xA4AD16EAL, 0xA06C0B5DL,
        0xD4326D90L, 0xD0F37027L, 0xDDB056FEL, 0xD9714B49L,
        0xC7361B4CL, 0xC3F706FBL, 0xCEB42022L, 0xCA753D95L,
        0xF23A8028L, 0xF6FB9D9FL, 0xFBB8BB46L, 0xFF79A6F1L,
        0xE13EF6F4L, 0xE5FFEB43L, 0xE8BCCD9AL, 0xEC7DD02DL,
        0x34867077L, 0x30476DC0L, 0x3D044B19L, 0x39C556AEL,
        0x278206ABL, 0x23431B1CL, 0x2E003DC5L, 0x2AC12072L,
        0x128E9DCFL, 0x164F8078L, 0x1B0CA6A1L, 0x1FCDBB16L,
        0x018AEB13L, 0x054BF6A4L, 0x0808D07DL, 0x0CC9CDCAL,
        0x7897AB07L, 0x7C56B6B0L, 0x71159069L, 0x75D48DDEL,
        0x6B93DDDBL, 0x6F52C06CL, 0x6211E6B5L, 0x66D0FB02L,
        0x5E9F46BFL, 0x5A5E5B08L, 0x571D7DD1L, 0x53DC6066L,
        0x4D9B3063L, 0x495A2DD4L, 0x44190B0DL, 0x40D816BAL,
        0xACA5C697L, 0xA864DB20L, 0xA527FDF9L, 0xA1E6E04EL,
        0xBFA1B04BL, 0xBB60ADFCL, 0xB6238B25L, 0xB2E29692L,
        0x8AAD2B2FL, 0x8E6C3698L, 0x832F1041L, 0x87EE0DF6L,
        0x99A95DF3L, 0x9D684044L, 0x902B669DL, 0x94EA7B2AL,
        0xE0B41DE7L, 0xE4750050L, 0xE9362689L, 0xEDF73B3EL,
        0xF3B06B3BL, 0xF771768CL, 0xFA325055L, 0xFEF34DE2L,
        0xC6BCF05FL, 0xC27DEDE8L, 0xCF3ECB31L, 0xCBFFD686L,
        0xD5B88683L, 0xD1799B34L, 0xDC3ABDEDL, 0xD8FBA05AL,
        0x690CE0EEL, 0x6DCDFD59L, 0x608EDB80L, 0x644FC637L,
        0x7A089632L, 0x7EC98B85L, 0x738AAD5CL, 0x774BB0EBL,
        0x4F040D56L, 0x4BC510E1L, 0x46863638L, 0x42472B8FL,
        0x5C007B8AL, 0x58C1663DL, 0x558240E4L, 0x51435D53L,
        0x251D3B9EL, 0x21DC2629L, 0x2C9F00F0L, 0x285E1D47L,
        0x36194D42L, 0x32D850F5L, 0x3F9B762CL, 0x3B5A6B9BL,
        0x0315D626L, 0x07D4CB91L, 0x0A97ED48L, 0x0E56F0FFL,
        0x1011A0FAL, 0x14D0BD4DL, 0x19939B94L, 0x1D528623L,
        0xF12F560EL, 0xF5EE4BB9L, 0xF8AD6D60L, 0xFC6C70D7L,
        0xE22B20D2L, 0xE6EA3D65L, 0xEBA91BBCL, 0xEF68060BL,
        0xD727BBB6L, 0xD3E6A601L, 0xDEA580D8L, 0xDA649D6FL,
        0xC423CD6AL, 0xC0E2D0DDL, 0xCDA1F604L, 0xC960EBB3L,
        0xBD3E8D7EL, 0xB9FF90C9L, 0xB4BCB610L, 0xB07DABA7L,
        0xAE3AFBA2L, 0xAAFBE615L, 0xA7B8C0CCL, 0xA379DD7BL,
        0x9B3660C6L, 0x9FF77D71L, 0x92B45BA8L, 0x9675461FL,
        0x8832161AL, 0x8CF30BADL, 0x81B02D74L, 0x857130C3L,
        0x5D8A9099L, 0x594B8D2EL, 0x5408ABF7L, 0x50C9B640L,
        0x4E8EE645L, 0x4A4FFBF2L, 0x470CDD2BL, 0x43CDC09CL,
        0x7B827D21L, 0x7F436096L, 0x7200464FL, 0x76C15BF8L,
        0x68860BFDL, 0x6C47164AL, 0x61043093L, 0x65C52D24L,
        0x119B4BE9L, 0x155A565EL, 0x18197087L, 0x1CD86D30L,
        0x029F3D35L, 0x065E2082L, 0x0B1D065BL, 0x0FDC1BECL,
        0x3793A651L, 0x3352BBE6L, 0x3E119D3FL, 0x3AD08088L,
        0x2497D08DL, 0x2056CD3AL, 0x2D15EBE3L, 0x29D4F654L,
        0xC5A92679L, 0xC1683BCEL, 0xCC2B1D17L, 0xC8EA00A0L,
        0xD6AD50A5L, 0xD26C4D12L, 0xDF2F6BCBL, 0xDBEE767CL,
        0xE3A1CBC1L, 0xE760D676L, 0xEA23F0AFL, 0xEEE2ED18L,
        0xF0A5BD1DL, 0xF464A0AAL, 0xF9278673L, 0xFDE69BC4L,
        0x89B8FD09L, 0x8D79E0BEL, 0x803AC667L, 0x84FBDBD0L,
        0x9ABC8BD5L, 0x9E7D9662L, 0x933EB0BBL, 0x97FFAD0CL,
        0xAFB010B1L, 0xAB710D06L, 0xA6322BDFL, 0xA2F33668L,
        0xBCB4666DL, 0xB8757BDAL, 0xB5365D03L, 0xB1F740B4L
    };
}
